The present invention relates generally to threaded screw fasteners, and more particularly to a new and improved threaded screw fastener or clamping screw that has a varying wave form in the helical thread pattern.
Simple threaded fasteners include male and female threaded components that engage one another to secure multiple items to each other. Threaded fasteners are used in widely differing applications, environments and conditions for widely varying purposes. Fasteners can be made of many different materials, both soft and hard, including various metals and plastics.
Thread patterns may vary, but typically they are based on a straight-line helix pattern. Thread pitch may vary from one type or size of fastener to another, and may even vary on different portions of the same fastener. The pitch of the male thread is typically provided at equal to or less than a basic pitch, and the female thread is typically provided at equal to or more than the basic pitch. As such, the male thread generally “floats” within the female thread, allowing the two components to be run together throughout the thread length with little or no interference until clamping pressure is applied during final tightening of the fastener.
It is known to provide threaded connections for use in electrical bus bars and connection terminals on, for example, electrical components, panel boards and the like. A wire is inserted into an aperture (terminal opening) and secured in the aperture by a clamping screw that is threaded into a transverse (threaded) opening. The screw binds the wire against the side of the aperture, opposite the threaded opening.
Often the bus bars or connection terminals (terminal strips or blocks) will have multiple connections on a single terminal strip. Clamping screws are provided on the terminal strip for one or more of the threaded openings that thread into the aperture.
When an electrical device is manufactured, it may include multiple terminal strips for terminating electrical conductors to the device. Screws are usually preinstalled and screwed all the way down into in their respective threaded apertures to prevent inadvertent loosening of the screws. In order to make the connections, the user must back-out each screw from its threaded opening a sufficient distance to insert the wire or electrical conductor through the aperture. The screw is then re-tightened to clamp the wire in place. This is a time consuming and labor intensive task.
One way to save time and cost is to have the screws only partially threaded into the terminal strip to preclude backing out the screws before inserting the wire. However, conventional screws will generally be loose in the threaded openings and, as such, may inadvertently back or fall out of the mating hole. This further increases installation time when the user or installer must find and place the lost screw or another screw in the threaded opening and then clamp the wire in place.
Clamp screws are known that provide an interference fit in the threaded opening to prevent inadvertent back-out. One such screw provides an anti hack-out feature when the screw is partially threaded into the opening, which then decreases when the screw is threaded sufficiently beyond the interference feature. While this may function in a satisfactory manner for certain applications, there are conditions under which decreasing the back-out force (which also results in a decrease in the insertion torque required) is not desired. For example, such an arrangement may not permit reusing the connection arrangement or permit use of the connection arrangement with different gauge conductors (wires).
Accordingly, there is a need for a new threaded fastener that addresses the foregoing problems and other problems of known fasteners. More particularly, there is a need for a new threaded fastener that provides the desired amount of back-out torque and insertion torque for a chosen application. There is a further need for a new threaded fastener that is capable of being installed in a pre-assembly position, that is configured to remain secured to the mating member while in the preassembly position, and that is adapted to be further threaded into the mating member to a final position under the appropriate insertion torque. More specifically, there is a need for a new threaded fastener for use in securing electrical connectors (wires) in terminal strips and blocks. Desirably, such a fastener provides an interference fit in a threaded opening that intersects the aperture into which the wire or connector is inserted. Such a fastener provides a desired amount of torque to tighten the fastener into the opening, while also maintaining the desired torque-tension relationship during the fastening sequence. Such a fastener is maintained tight in the threaded opening to facilitate efficient use of preassembled field ready components. Such a fastener is also reusable and is usable with different sizes (gauges) of wire.